Disabled persons who are confined to wheelchairs have often found their mobility and, hence, their activities limited by the capabilities of the wheelchairs available to them. The efforts of architects and planners to make public places and private spaces accessible to the wheelchair-bound can be thwarted by the limitations of the very wheelchairs on which the handicapped must depend for access to all parts of their environment. Currently, available wheelchairs include those that are motor driven and those that are driven manually. The high cost of motor driven wheelchairs, which are powerful enough to negotiate many different types of surfaces and terrains, puts them beyond the reach of large numbers of those who need them. The available manually driven wheelchairs, moreover, are often difficult to drive, especially up inclines, over curbs and on uneven terrain. In addition, the majority of these wheelchairs restrict the user to a sitting position. Those wheelchairs that enable their users to assume a standing position are expensive, complex and uncomfortable.
The design of currently available manually driven wheelchairs, moreover, presents many disadvantages and limitations. Two large drive wheels, which are usually positioned on each side near the center of gravity of the wheelchair, support the wheelchair and contact the ground, floor or other base surface on which the wheelchair rests. These large wheels are moved by the user's hands to propel the wheelchair in the direction desired. This is difficult for many infirm wheelchair occupants, as the large wheels on most wheelchairs are located at the rear of the chair, and the occupant must reach back to grasp and propel the wheel. This requires an upper body strength that many handicapped and infirm persons do not have.
Additionally, because the user must usually contact the large drive wheels directly to propel the wheelchair, the user's hands and clothing tend to become soiled during travel, particularly during inclement weather and during travel over surfaces covered with dirt, oil, or other foreign matter which can be picked up by the wheelchair wheels.
To avoid the problems presented by dirt and foreign matter carded by the wheels of a wheelchair, handwheels have been provided which do not contact the wheelchair support surface but which are linked to the wheelchair wheels by a propulsion linkage system. U.S. Pat. Nos. 2,181,420 to Everest et al, 4,380,343 to Lovell et al and 4,625,984 to Kitrell disclose wheelchairs driven by hand wheels which are manually rotated by the wheelchair occupant to drive ground contacting wheels and propel the chair. However, the practice has been to position these handwheels toward the center or rear of the chair, thereby requiring the wheelchair occupant to reach back to grasp the leading edge of the handwheel.
It has been found that less upper body strength is required to propel a wheelchair if the occupant is reaching forward from a sitting position and is propelling the wheelchair by moving the arms from a partially to a fully extended forward position. In an attempt to take advantage of this fact, wheelchairs have been developed with manual drives positioned forwardly of the wheelchair seat. U.S. Pat. Nos. 287,789 to Arbogast and 4,758,013 to Agrrillo are illustrative of powered wheelchairs of this type, but it will be noted that these forwardly positioned wheelchair drives are dual crank drives. Dual crank drives make it difficult for a wheelchair occupant to synchronize the cranking power provided to opposite cranks and require power to be provided by a rotary motion of the arms rather than by the pushing motion used to turn a handwheel. This rotary motion is difficult for many infirm persons to achieve for prolonged periods with sufficient energy to propel the wheelchair.
To allow the wheelchair user virtually unlimited mobility, the chair should support the user adequately in a sitting position for travel. The chair should, in addition, permit the user to assume a standing position supported as needed by the wheelchair in a manner that permits the user to use and, thus, strengthen those parts of the body which he or she is capable of using. Wheelchairs that adjust to support the occupant in both a sitting and a standing position are known. For example, the wheelchair disclosed in U.S. Pat. No. 4,809,804 to Houston et al. achieves this objective. However, the seat assembly in this patent is a complex, motor driven apparatus that leaves the occupant in an extremely uncomfortable upright position with only limited mobility.
In moving a wheelchair occupant from a sitting to a standing position, it is critical that both positions provide adequate and comfortable support if the wheelchair is to function efficiently. It is substantially useless to suspend an occupant uncomfortably from a chest strap assembly in a standing position as often occurs if the user of the chair is a paraplegic or a multiple amputee. The chair should be designed to distribute pressure to the back, buttocks and thighs of a user in the standing position. Also, as the chair moves an occupant from a sitting to a standing position, it is often critical that the chair backrest not apply shear stresses to the back of an occupant.